Citric acid is a common material of natural origin. The structure is:
                CAS Registry number: 77-92-9        CAS Index name: 1,2,3-Propanetricarboxylic acid        
Citric acid is made during the fermentation process; using cultures of Aspergillus niger are fed on a sucrose or glucose-containing medium.
Citric acid is one of a series of compounds involved in the physiological oxidation of fats, proteins, and carbohydrates to carbon dioxide and water. This series of chemical reactions is central to nearly all metabolic reactions, and is the source of two-thirds of the food-derived energy in higher organisms. Krebs received the 1953 Nobel Prize in physiology or Medicine for the discovery. The series of reactions is known by various names including, citric acid cycle, the Krebs cycle, and the tricarboxylic acid cycle.
Citrate esters are also well known. They conform to the following structure:
These esters are made by the reaction of citric acid with alcohols.
U.S. Pat. No. 4,292,192 issued to Hooper et al. teaches that detergent bars for personal washing are given a deodorant property by including an ester of citric acid. The ester maybe an acetyl derivative. The amount of ester used will be in the range of 0.3% to 3.0%. Examples of the esters are triethyl citrate and acetyl tributyl citrate.
An article published in Cosmetic and Toiletries Magazine (Vol. 110 August 1995) by O'Lenick et al addresses Guerbet Citrate Esters. It specifically deals with oil phase emollient esters and breathable non occlusive esters that have fluoro components contained in the ester. Both type of esters are hydrophobic (i.e. oil loving). This article discloses the state of the art of citrate esters, specifically as oil soluble materials that can be applied to skin. The article is posted on http://www.surfatech.com/pdfs/Guerbet%20Citrate%20Ester%20Article.pdf
The ability to make compounds having differing solubility in water allows one to make surface active agents, or surfactants. The proper selection of the ratio of water soluble to oil soluble material in the molecule allows for the manufacture of emulsifiers useful over a wide range of formulations.
HLB is a methodology that explains this phenomenon. The method was developed by Griffin in 1954 and relates an estimation of surfactant properties to the percentage of water soluble group in a molecule. Specifically, the system addresses polyoxyethylene groups in a non-ionic surfactant/HLB=% PEG in the molecule/5HLB value of 0 corresponds to a completely hydrophobic molecule, and a value of 20 would correspond to a molecule made up completely of hydrophilic components.The HLB value can be used to predict the surfactant properties of a molecule:A value from 4 to 8 indicates an anti-foaming agentA value from 7 to 11 indicates a W/O (water in oil) emulsifierA value from 12 to 16 indicates oil in water emulsionA value from 11 to 14 indicates a wetting agentA value from 12 to 15 is typical of detergentsA value of 16 to 20 indicates a solubiliser or hydrotrope.
The citrate esters known prior to the compounds of the present invention are oil phases. It was previously unappreciated that by making specific heretofore unknown esters, a series of citrate esters could be developed that are emulsifiers. There has been a long felt need for emulsifiers that provide excellent emulsification and citrate esters have not been available that had any water soluble groups, until this invention.